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Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic Properties

Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic... magnetochemistry Article Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic Properties 1 , 2 , 1 , 3 2 , 4 5 4 4 Lucie Zárybnická * , Martin Marek , Radek Ševc ˇík , Radek Stolín , Jaroslav Pokorný and Jir ˇí Šál Department of Technical Studies, College of Polytechnics Jihlava, Tolstého 16, 586 01 Jihlava, Czech Republic Institute of Theoretical and Applied Mechanics of the Czech Academy of Sciences, Centre Telc, ˇ Prosecká 809/76, 190 00 Praha 9, Czech Republic IT4Innovations, Technical University of Ostrava, Studentská 6231/1B, 708 00 Ostrava-Poruba, Czech Republic Department of Civil Engineering, Faculty of Technology, Institute of Technology and Business, Okružní 517/10, 370 01 Ceské Budejovice, ˇ Czech Republic Department of Mathematics, College of Polytechnics Jihlava, Tolstého 16, 586 01 Jihlava, Czech Republic * Correspondence: [email protected] Abstract: This work aims to characterize printing structures with various infill densities composed of a thermoplastic material containing magnetic particles composed of mainly Iron(III) oxides with regard to their possible processing with the additive technology of Fused Filament Fabrication. A polyethylene terephthalate glycol (PET-G) structural thermoplastic with the addition of Iron(III)) oxides has been selected, and correct processing temperatures have been determined using thermal analysis. The paramagnetic properties of printed products consisting of different filling densities have been tested. Relative permeability has been identified to be strongly dependent on the printed internal structures of tested products. The samples composed of the densest structure have shown relative permeability higher by 18% with respect to the sample printed with the least dense structure. Finite Element Modelling (FEM) simulations have been applied to determine magnetic field distributions and, moreover, to calculate the holding forces of all printed samples. The performed simulations confirmed that produced composites might be utilized as magnetic switches and sensors or as more advanced components for homogenizing electric motors’ magnetic fields. Moreover, magnetic properties might be tuned according to the specific needs printing structure with the suitable density. Citation: Zárybnická, L.; Marek, M.; Ševcík, ˇ R.; Stolín, R.; Pokorný, J.; Šál, Keywords: 3D printing; FFF; PET-G; iron(III) oxide; magnetic properties; FEM simulation J. Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic Properties. Magnetochemistry 2023, 9, 2. 1. Introduction https://doi.org/10.3390/ Nowadays, additive manufacturing is intensively applied in medicine [1–3], re- magnetochemistry9010002 search [4], engineering [5–7], civil engineering [8], food industries [9], and other industrial Academic Editor: Greg A. Brewer sectors. It represents a prominent way of processing various types of materials [10]. One Received: 22 November 2022 of the most widely used technologies, common in the industry as well as in hobby usage, Revised: 15 December 2022 is Fused Filament Fabrication (FFF), developed by S. Scott Crump in 1989 [11], which Accepted: 18 December 2022 processes filament materials composed of thermoplastics or elastomers. Published: 22 December 2022 FFF additive technology offers a wide range of benefits, such as affordability, suit- ability for both commercial and hobby applications, accessibility of processing materials, and usability for shape-demanding products. An inexhaustible number of different types of thermoplastics and elastomers are currently available for processing. Polylactic acid Copyright: © 2022 by the authors. (PLA) [12–14], polyethylene terephthalate (PET) [15–18], polyethylene terephthalate gly- Licensee MDPI, Basel, Switzerland. col (PET-G) [15,16,19–22], acrylonitrile butadiene styrene (ABS) [23–26], polypropylene This article is an open access article (PP) [27–30], polycarbonate (PC) [31,32], and polyvinylchloride (PVC) [33] belong to the distributed under the terms and most common thermoplastics suitable for processing. conditions of the Creative Commons To improve and/or modify the properties of polymeric materials according to the Attribution (CC BY) license (https:// specific need of their application, various types of additives like UV stabilizers, various creativecommons.org/licenses/by/ fillers, flame retardants, or pigments [34,35] are commonly applied. Last but not least, 4.0/). Magnetochemistry 2023, 9, 2. https://doi.org/10.3390/magnetochemistry9010002 https://www.mdpi.com/journal/magnetochemistry Magnetochemistry 2023, 9, 2 2 of 12 certain additives are also used to improve the magnetic properties of the material. In general, fillers can be applied in the form of particles or fibers. Magnetic particles impart magnetic properties to the polymer composite, conductance, and shielding properties when the basic characteristics describing magnetic properties include magnetic induction, magnetic field intensity, and relative permeability of the material. In this work, PET-G, providing products with, e.g., excellent mechanical properties, ease of use, and sufficient resistance to higher temperatures (compared to the thermoplas- tics ABS and PLA) [36–38], was used. In addition, PET-G usually provides outstanding adhesion between the layers. Moreover, it has minimal risk of twisting and limited shrink- age and can be recycled [39]. PET-G is non-magnetic, which limits its usage for specific applications like components designed to guide and concentrate magnetic flux [40–42] or concentrate magnetic force [43,44]. For these reasons, products containing Iron(III) oxides are used to provide magnetically detectable thermoplastic (MDT) PET-G for the manufacture of sensors and intelligent packaging. This work focused on optimizing the filling density of printed structures composed of PET-G-containing Iron(III) oxides with regard to maintaining the required magnetic characteristics (sufficient permeability values) and material demands needed for processing. Subsequently, the magnetic behavior of developed materials was additionally evaluated by applying Finite Element Modelling (FEM). 2. Materials and Methods 2.1. Materials Grey filaments composed of PET-G containing Iron(III) oxides (Smart Materials 3D, Spain) were used to prepare 3D test samples for subsequent property analysis. The reference sample was printed from black filaments composed of PET-G without magnetic additives (Ø 1.75  0.05 mm, Plasty Mladec, Czech Republic) with a density of 1.27 g.cm . Before usage, materials were conditioned at 50 C for 5 h to remove absorbed water [45]. 2.2. Praparation of Samples The samples were printed as circles (see Figure 1) with a diameter of 60/50 mm (outer/inner) and a height of 20 mm. This shape is conventional for samples used to determine the magnetic properties of ferromagnetic materials using the toroid measurement method [46–50]. A gyroid structure with an infill density of 0, 20, 50, 80, and 100% (Figure 1) was selected. Samples containing the additive were marked according to the filling, namely 0A, 20A, 50A, 80A, and 100A. The reference sample was prepared without any additive with 100% density filling and marked as 100F. The printing temperature was 235 C, whereas the plate temperature was 85 C. The 3D print speed was set to 70 mms . The layer thickness was 0.2 mm, extrusion width 0.4 mm, and skin thickness 0.6 mm—With 1 contour layer. A 3D nozzle with a hole diameter of 0.4 mm was used. Table 1 summarizes all relevant parameters (e.g., printing time and volumes) of the produced samples. At least two duplicates were produced for each sample type. Table 1. Summarization of printing processes for all produced samples. Sample Infill Density/% Printing Time Weight of Filament/g Price/EUR * 0A 0 38 min 3 s 11.3 0.87 20A 20 45 min 8 s 14.2 1.09 50A 50 57 min 38 s 17.0 1.31 80A 80 71 min 5 s 19.4 1.49 100A 100 61 min 34 s 22.9 1.76 100F 100 61 min 34 s 20.4 0.55 * Prices are given as of 14 November 2022. Magnetochemistry 2023, 9, 2 3 of 12 Magnetochemistry 2023, 9, x FOR PEER REVIEW 3 of 13 Figure 1. A diagram of the structures of the prepared samples: (A)—0% filling density, (B)—20% Figure 1. A diagram of the structures of the prepared samples: (A)—0% filling density, (B)—20% filling density, (C)—50% filling density, (D)—80% filling density, (E)—100% filling density. The filling density, (C)—50% filling density, (D)—80% filling density, (E)—100% filling density. The details details of the respective individual types of filling are shown at the bottom right (labeled accord- of the respective individual types of filling are shown at the bottom right (labeled according to the ing to the specific sample). specific sample). Table 1. Summarization of printing processes for all produced samples. 2.3. Methods 3D printing was performed on DeltiX (TriLAB, Czech Republic, nozzle size 0.4 mm), Sample Infill Density/% Printing Time Weight of Filament/g Price/EUR * implementing the FFF technique. A working area of (250  300) mm with an integrated 0A 0 38 min 3 s 11.3 0.87 LCD was applied. Models were created and edited by the FreeCad software and exported in 20A 20 45 min 8 s 14.2 1.09 the .stl format (stereolithography). PrusaSlicer 2.2.0 was used to set the printing parameters 50A 50 57 min 38 s 17.0 1.31 and export them to a post-processing format (*g-code format). 80A 80 71 min 5 s 19.4 1.49 The cross-section of filaments was characterized in terms of surface quality using a 100A 100 61 min 34 s 22.9 1.76 Keyence VHX-6000 optical microscope (Keyence, Itasca, MN, USA) and inspected at 2500 100F 100 61 min 34 s 20.4 0.55 magnification with a focus on the additive distribution. * Prices are given as of 14 November 2022. Additive powders were analyzed for particle size using Keyence VHX-6000 optical microscope (Keyence, Itasca, MN, USA) at 1000 magnification with subsequent analysis 2.3. Methods in the software ImageJ. 3D printing was performed on DeltiX (TriLAB, Czech Republic, nozzle size 0.4 mm), Analyzing the thermal behavior (mass change, heat flow) of the filament samples was implementing the FFF technique. A working area of (250 × 300) mm with an integrated followed by simultaneously performing a Thermogravimetry analysis (TGA) and Differen- LCD was applied. Models were created and edited by the FreeCad software and exported tial thermal analysis (DTA) under non-isothermal conditions, using a TGA 2 instrument in the .stl format (stereolithography). PrusaSlicer 2.2.0 was used to set the printing param- (Mettler-Toledo, Columbus, OH, USA). The measurements were performed in a nitrogen eters and export them to a post-processing format (*g-code format). atmosphere at a heating rate of 20 Cmin , in the temperature range of 30–450 C. The The cros determination s-section of of the filame additive nts was ch content aracte was rize carried d in te out rmon s othe f sur basis face qu of the alitstandar y using a d CSN Keyence EN ISO VHX-6000 optical m 3451-1 [51]. Thr iee croscope replicates (Keyence were ,used Itasca, for M determination. N, USA) and insp The ecte pr d ocedur at 2500 e× magnification with a focus on the additive distribution. consisted of the determination of the combustible proportions when additive content (w, wt.%)Addi usedtive po the calculation wders were by Equation analyzed for p (1): article size using Keyence VHX-6000 optical microscope (Keyence, Itasca, MN, USA) at 1000× magnification with subsequent analysis in the software ImageJ. w = 1  100, (1) Analyzing the thermal behavior (mass change, heat flow) of the filament samples was followed by simultaneously performing a Thermogravimetry analysis (TGA) and Dif- where m is the weight after combustion (g), m is the weight before combustion (g). 1 2 ferential thermal analysis (DTA) under non-isothermal conditions, using a TGA 2 instru- The morphology of samples was investigated with a scanning electron microscope ment (Mettler-Toledo, Columbus, OH, USA). The measurements were performed in a ni- (SEM) Quanta 450 FEG (FEI, Czech Republic) using a secondary electron detector. Observa- −1 trogen atmosphere at a heating rate of 20 °C∙min , in the temperature range of 30–450 °C. tions were conducted on fractured surfaces at 20 kV accelerating voltage. Samples were The determination of the additive content was carried out on the basis of the standard placed on carbon tape and gold coated with a 7 nm thick layer. ČSN EN ISO 3451-1 [51]. Three replicates were used for determination. The procedure X-ray powder diffraction (XRPD) data were collected at 40 kV and 40 mA with a Bragg– consisted of the determination of the combustible proportions when additive content (w, Brentano - diffractometer (Bruker D8 Advance, USA, Cu K radiation ( = 1.5418 Å)). wt.%) used the calculation by Equation (1): Data were collected in the angular range 8–80 2 counting 0.4 s for each step of 0.0102 Magnetochemistry 2023, 9, x FOR PEER REVIEW 4 of 13 𝑚1 (1) 𝑤=(1− )∗100, 𝑚2 where m1 is the weight after combustion (g), m2 is the weight before combustion (g). The morphology of samples was investigated with a scanning electron microscope (SEM) Quanta 450 FEG (FEI, Czech Republic) using a secondary electron detector. Obser- vations were conducted on fractured surfaces at 20 kV accelerating voltage. Samples were placed on carbon tape and gold coated with a 7 nm thick layer. X-ray powder diffraction (XRPD) data were collected at 40 kV and 40 mA with a Bragg–Brentano θ-θ diffractometer (Bruker D8 Advance, USA, Cu Kα radiation (λ = 1.5418 Å)). Data were collected in the angular range 8–80° 2θ counting 0.4 s for each step of 0.0102° 2θ. Rietveld refinements were used for quantitative phase analysis (QPA) using TOPAS 4.2 (Bruker AXS). Magnetic properties were measured on a Remagraph C-500 measuring device (Mag- net-Physik Dr. Steingroever Gmbh, Germany) designed to determine the quasi-stationary (DC) BH hysteresis characteristics of ferromagnetic materials. The configuration of the measuring system Remagraph version C500 is equipped with two electronic fluxmeters EF5. Furthermore, the Remagraph C500 is equipped with a precision DC power supply Magnetochemistry 2023, 9, 2 4 of 12 with a power of 320 VA and parameters ±40 V; ±8 A. The magnitude of the magnetic in- tensity and induction in the measured sample are determined, on the one hand, by the measured material itself and, on the other hand, by the winding configuration (Figure 2). The windings on the samples were made with an insulated copper conductor of full cross- 2. Rietveld refinements were used for quantitative phase analysis (QPA) using TOPAS 4.2 section, where the conductor’s designation was U2 × 0.5. (Bruker AXS). In principle, the magnetizing winding of the measured toroid is connected to a direct Magnetic properties were measured on a Remagraph C-500 measuring device (Magnet- Physik currentDr sour . Steingr ce. The oever curren Gmbh, t is very Germany) slowly incre designed ased and subse to determine quently the de quasi-stationary creased to create (DC) a com BH plehyster te circul esis ation o characteristics f the entire BH of ferr char omagnetic acteristic. T materials. he measur The ing wind configuration ing is connected of the measuring to an electro system nic fluxm Remagraph eter which recor version C500 ds vois ltaequipped ge jitters on with the m twoeelectr asurin onic g win fluxmeters ding and EF5. integra Furthermor tes this vo e,ltthe age. B Remagraph y a joint ev C500 aluais tion o equipped f the ex with citati aon c precision urrent an DCd the power intsupply egrated with a power of 320 VA and parameters 40 V; 8 A. The magnitude of the magnetic voltage, we obtain the resulting BH characteristic—Either only the magnetization or the intensity and induction in the measured sample are determined, on the one hand, by the complete BH hysteresis characteristic [52,53]. An embodiment of the Remagraph measur- measured material itself and, on the other hand, by the winding configuration (Figure 2). ing system and its basic block diagram is shown in Figure 3. Figure 4 shows the principle The windings on the samples were made with an insulated copper conductor of full of determining the magnetic quantities and the individual connections in the toroidal cross-section, where the conductor ’s designation was U2  0.5. sample and the measured material. Figure 2. Photographic images of the testing samples for the magnetic properties measurement, (A)—Samples after 3D printing, (B)—Samples with winding configuration. In principle, the magnetizing winding of the measured toroid is connected to a direct current source. The current is very slowly increased and subsequently decreased to create a complete circulation of the entire BH characteristic. The measuring winding is connected to an electronic fluxmeter which records voltage jitters on the measuring winding and integrates this voltage. By a joint evaluation of the excitation current and the integrated voltage, we obtain the resulting BH characteristic—Either only the magnetization or the complete BH hysteresis characteristic [52,53]. An embodiment of the Remagraph measuring system and its basic block diagram is shown in Figure 3. Figure 4 shows the principle of determining the magnetic quantities and the individual connections in the toroidal sample and the measured material. A simulation program based on the principle of FEM methods, namely the Ansys- Maxwell software (Ansys Inc., Canonsburg, PA, USA), was used to evaluate the magnetic field and holding force of the typical configurations of the permanent magnet and the printed magnetic plastic disc. Ansys-Maxwell is an electromagnetic tool designed to analyze low-frequency problems and devices using the solution of general Maxwell’s equations. The actual simulation of the magnetic field was performed in the program Ansys-Maxwell using FEM calculation methods [54–56]. Magnetochemistry 2023, 9, x FOR PEER REVIEW 5 of 13 Magnetochemistry 2023, 9, x FOR PEER REVIEW 5 of 13 Magnetochemistry 2023, 9, 2 5 of 12 Figure 2. Photographic images of the testing samples for the magnetic properties measurement, Figure 2. Photographic images of the testing samples for the magnetic properties measurement, (A)—Samples after 3D printing, (B)—Samples with winding configuration. (A)—Samples after 3D printing, (B)—Samples with winding configuration. Figure 3. Graphical illustration of remagraph—The basic block diagram of a measuring system. Figure 3. Graphical illustration of remagraph—The basic block diagram of a measuring system. Figure 3. Graphical illustration of remagraph—The basic block diagram of a measuring system. Figure 4. The illustration of the principle of determination of magnetic quantities using toroidal Figure 4. The illustration of the principle of determination of magnetic quantities using toroidal samples. Figure 4. The illustration of the principle of determination of magnetic quantities using toroidal samples. samples. 3. Results and Discussion A simulation program based on the principle of FEM methods, namely the Ansys- A simulation program based on the principle of FEM methods, namely the Ansys- 3.1. Characterization of Material Maxwell software (Ansys Inc., Canonsburg, PA, USA), was used to evaluate the magnetic Maxwell software (Ansys Inc., Canonsburg, PA, USA), was used to evaluate the magnetic XRD analysis revealed that the applied magnetics additive was composed mainly of field and holding force of the typical configurations of the permanent magnet and the field and holding force of the typical configurations of the permanent magnet and the hematite (Iron(III) oxide; 70.7  0.2 wt.%) with 29.3  0.2 wt.% of rutile (Ti(II) dioxide) printed magnetic plastic disc. Ansys-Maxwell is an electromagnetic tool designed to ana- printed magnetic plastic disc. Ansys-Maxwell is an electromagnetic tool designed to ana- based on XRD analysis. Such a combination of mixed oxides compositions exhibits para- lyze low-frequency problems and devices using the solution of general Maxwell’s equa- lyze low-frequency problems and devices using the solution of general Maxwell’s equa- magnetic behavior at room temperature [57]. The mean particle size was calculated to be tions. The actual simulation of the magnetic field was performed in the program Ansys- tions. The actual simulation of the magnetic field was performed in the program Ansys- 160.2  15.3 nm (see Figure S1). The additive content (determined using the combustion Maxwell using FEM calculation methods [54–56]. Maxwell using FEM calculation methods [54–56]. process) was found to be 3.11  0.12 wt.%. The melting point (T ) of both PET-G filaments, with and without the content of metal 3. Results and Discussion 3. Results and Discussion oxides, were determined to select the correct processing temperatures of the extruder and 3.1. Characterization of Material the 3.1. C bed haracteri as wellzation of (Figure Mate S2). T rial he glass transition temperature for this material without addi- XRD analysis revealed that the applied magnetics additive was composed mainly of tives is around 80 C [58]. Setting the temperature around the glass transition temperature XRD analysis revealed that the applied magnetics additive was composed mainly of hematite (Iron(III) oxide; 70.7 ± 0.2 wt.%) with 29.3 ± 0.2 wt.% of rutile (Ti(II) dioxide) for bed temperatures is recommended. One of the first points mentioned in any extrusion hematite (Iron(III) oxide; 70.7 ± 0.2 wt.%) with 29.3 ± 0.2 wt.% of rutile (Ti(II) dioxide) based on XRD analysis. Such a combination of mixed oxides compositions exhibits para- discussion (FFF technology is based on the extrusion process) is the melt temperature. based on XRD analysis. Such a combination of mixed oxides compositions exhibits para- magnetic behavior at room temperature [57]. The mean particle size was calculated to be This is the only temperature that is absolute. The DTA-TGA technique is not sensitive to magnetic behavior at room temperature [57]. The mean particle size was calculated to be 160.2 ± 15.3 nm (see Figure S1). The additive content (determined using the combustion determine T ; therefore, only T was determined. The T was determined to be 244.02 C g m m 160.2 ± 15.3 nm (see Figure S1). The additive content (determined using the combustion process) was found to be 3.11 ± 0.12 wt.%. for the filament containing metal oxides and 235.87 C for the reference sample. process) was found to be 3.11 ± 0.12 wt.%. The melting point (Tm) of both PET-G filaments, with and without the content of The homogeneous distribution of this additive in the PET-G matrix was confirmed The melting point (Tm) of both PET-G filaments, with and without the content of metal oxides, were determined to select the correct processing temperatures of the ex- from its microscopic observations, as can be seen in Figure 5 and detailed in the enclosed in- metal oxides, were determined to select the correct processing temperatures of the ex- truder and the bed as well (Figure S2). The glass transition temperature for this material set figure. The SEM observations showed that applied metal oxides exhibit a high variety in truder and the bed as well (Figure S2). The glass transition temperature for this material shapes and sizes (Figure 6a). Nanosized particles together with micrometric agglomerates were observed. Observations at higher magnifications revealed that larger agglomerates Magnetochemistry 2023, 9, x FOR PEER REVIEW 6 of 13 without additives is around 80 °C [58]. Setting the temperature around the glass transition temperature for bed temperatures is recommended. One of the first points mentioned in any extrusion discussion (FFF technology is based on the extrusion process) is the melt temperature. This is the only temperature that is absolute. The DTA-TGA technique is not sensitive to determine Tg; therefore, only Tm was determined. The Tm was determined to be 244.02 °C for the filament containing metal oxides and 235.87 °C for the reference sam- ple. The homogeneous distribution of this additive in the PET-G matrix was confirmed from its microscopic observations, as can be seen in Figure 5 and detailed in the enclosed inset figure. The SEM observations showed that applied metal oxides exhibit a high vari- Magnetochemistry 2023, 9, 2 6 of 12 ety in shapes and sizes (Figure 6a). Nanosized particles together with micrometric ag- glomerates were observed. Observations at higher magnifications revealed that larger ag- glomerates were composed of nanosized, mainly spherulitic, particles (Figure 6b). The wer intern e composed al structure of nanosized, of the PET-G mainly sample spher witho ulitic,u partic t meta les l p (Figur articles e 6 i b). s visu Theainternal lized in F str iuc- gure 6c. tur Fig e u of re 6d the PET confirmed -G sample the homogenous without metal dis particles tributi is ons visualized of metal in pa Figur rticles e 6w c.ithin a polymer Figure 6d confirmed the homogenous distributions of metal particles within a polymer matrix. matrix. Magnetochemistry 2023, 9, x FOR PEER REVIEW 7 of 13 Figure 5. Microscopic image of the microstructure of the used PET-G filament containing metal Figure 5. Microscopic image of the microstructure of the used PET-G filament containing metal oxides. oxides. Figure 6. The collection of SEM images: (a)—Particles of metal oxides observed at lower magnifi- Figure 6. The collection of SEM images: (a)—Particles of metal oxides observed at lower magnifica- cation,(b)—Microstructure of metal oxides particles observed at higher magnification, (c)—Inter- tion, (b)—Microstructure of metal oxides particles observed at higher magnification, (c)—Internal nal structure of PET-G sample, (d)—Internal structure of PET-G sample containing additive. structure of PET-G sample, (d)—Internal structure of PET-G sample containing additive. 3.2. Magnetic Properties As expected, the prepared PET-G samples containing magnetic fillers showed para- magnetic behavior [59]. The measured BH hysteresis characteristic is thus reduced to a straight line, and the resulting characteristic magnetic parameter corresponds to the rela- tive permeability. Figure 7 shows the magnetization characteristics for all types of pro- duced samples with 0–100% filling density. The clear difference between samples 100A and 100F (REF) is visible. In the case of sample A, only small differences can be observed with the increasing filling density. A determined value of relative permeability was found to increase slightly with higher filling density: 1.24, 1.29, 1.34, 1.35, and 1.39 for samples 0A, 20A, 50A, 80A, and 100A, respectively. Such values were determined to be at least 18 % higher if compared with the REF sample (1.05). Figure 7. Resulting in magnetization characteristics of individual samples. Magnetochemistry 2023, 9, x FOR PEER REVIEW 7 of 13 Figure 6. The collection of SEM images: (a)—Particles of metal oxides observed at lower magnifi- cation,(b)—Microstructure of metal oxides particles observed at higher magnification, (c)—Inter- nal structure of PET-G sample, (d)—Internal structure of PET-G sample containing additive. Magnetochemistry 2023, 9, 2 7 of 12 3.2. Magnetic Properties As expected, the prepared PET-G samples containing magnetic fillers showed para- 3.2. Magnetic Properties magnetic behavior [59]. The measured BH hysteresis characteristic is thus reduced to a As expected, the prepared PET-G samples containing magnetic fillers showed para- straight line, and the resulting characteristic magnetic parameter corresponds to the rela- magnetic behavior [59]. The measured BH hysteresis characteristic is thus reduced to a tive permeability. Figure 7 shows the magnetization characteristics for all types of pro- straight line, and the resulting characteristic magnetic parameter corresponds to the relative duced samples with 0–100% filling density. The clear difference between samples 100A permeability. Figure 7 shows the magnetization characteristics for all types of produced and 100F (REF) is visible. In the case of sample A, only small differences can be observed samples with 0–100% filling density. The clear difference between samples 100A and 100F with the increasing filling density. A determined value of relative permeability was found (REF) is visible. In the case of sample A, only small differences can be observed with the to incr incr ea easing se slig filling htly wi density th higher f . A determined illing densi value ty: 1.of 24r, elative 1.29, 1. permeability 34, 1.35, and was 1.39 found for sam to ples increase slightly with higher filling density: 1.24, 1.29, 1.34, 1.35, and 1.39 for samples 0A, 0A, 20A, 50A, 80A, and 100A, respectively. Such values were determined to be at least 18 20A, 50A, 80A, and 100A, respectively. Such values were determined to be at least 18 % % higher if compared with the REF sample (1.05). higher if compared with the REF sample (1.05). Figure 7. Resulting in magnetization characteristics of individual samples. Figure 7. Resulting in magnetization characteristics of individual samples. 3.3. Magnetic Field Simulation and Calculation of Force Effects The basic possible usage of printed magnetic plastics is related to the emergence of a certain force effect on the finished material upon its exposure to an external magnetic field [60]. In common and technical practice, there are certainly applications where it is necessary to attach a general plastic structure to a magnet or other source of a magnetic field. Conversely, attaching the magnetic elements to the plastic base may also be beneficial. In simple terms, it may be an alternative to a sheet metal magnetic board. The key question for subsequent practical applications is how large can be the achieved force. The find the answer to this question, this subchapter presents the results of the magnetic field simulation and calculation of force effects on the model of the selected type configuration of a permanent magnet and type plastic plate corresponding to variants of printed PET-G with different levels of filling. During the simulation, different distances of the magnet from the plastic plate, ranging from 0 to 5 mm, were considered. The model was conceived as 2D axisymmetric and corresponded to the cylindrical design of the permanent magnet and the plastic plate. The permanent magnet had a diameter of 20 mm and a height of 3 mm. The plastic plate with a magnetic filler had a diameter of 100 mm and a thickness of 5 mm. The surroundings of the model were air with a diameter of 240 mm and a height of 120 mm. The permanent magnet was considered to be the FeNdB type, version N35, with a coercive force (Hc) equal to 890 Kam . The design of the model is graphically visualized in Figures 8 and 9, where the basic model for the zero distance of the magnet and the plastic plate is shown. Magnetochemistry 2023, 9, x FOR PEER REVIEW 8 of 13 3.3. Magnetic Field Simulation and Calculation of Force Effects The basic possible usage of printed magnetic plastics is related to the emergence of a certain force effect on the finished material upon its exposure to an external magnetic field [60]. In common and technical practice, there are certainly applications where it is neces- sary to attach a general plastic structure to a magnet or other source of a magnetic field. Conversely, attaching the magnetic elements to the plastic base may also be beneficial. In simple terms, it may be an alternative to a sheet metal magnetic board. The key question for subsequent practical applications is how large can be the achieved force. The find the answer to this question, this subchapter presents the results of the magnetic field simula- tion and calculation of force effects on the model of the selected type configuration of a permanent magnet and type plastic plate corresponding to variants of printed PET-G with different levels of filling. During the simulation, different distances of the magnet from the plastic plate, rang- ing from 0 to 5 mm, were considered. The model was conceived as 2D axisymmetric and corresponded to the cylindrical design of the permanent magnet and the plastic plate. The permanent magnet had a diameter of 20 mm and a height of 3 mm. The plastic plate with a magnetic filler had a diameter of 100 mm and a thickness of 5 mm. The surroundings of the model were air with a diameter of 240 mm and a height of 120 mm. The permanent magnet was considered to be the FeNdB type, version N35, with a coercive force (Hc) −1 Magnetochemistry 2023, 9, 2 equal to 890 Ka·m . The design of the model is graphically visualized in Figures 8 and 9, 8 of 12 where the basic model for the zero distance of the magnet and the plastic plate is shown. Magnetochemistry 2023, 9, x FOR PEER REVIEW 9 of 13 Figure 8. The FEM model of the permanent magnet and plastic plate with a magnetic filler. Figure 8. The FEM model of the permanent magnet and plastic plate with a magnetic filler. Figure 9. An image of a computer network model. Figure 9. An image of a computer network model. The actual FEM calculation of the magnetic field distribution corresponds to a magne- The actual FEM calculation of the magnetic field distribution corresponds to a mag- tostatic problem with excitation using permanent magnets [54–56]. netostatic problem with excitation using permanent magnets [54–56]. The result of the simulations is the distributions of the magnetic field in the magnet The result of the simulations is the distributions of the magnetic field in the magnet and the plastic plate with the magnetic filler and the surrounding air. The distribution of and the plastic plate with the magnetic filler and the surrounding air. The distribution of magnetic field intensity (H) and magnetic induction (B) for the model with zero air gap magnetic field intensity (H) and magnetic induction (B) for the model with zero air gap are shown in Figures 10 and 11, respectively. The magnitude of the applied force on the are shown in Figures 10 and 11, respectively. The magnitude of the applied force on the plastic plate is then obtained by post-processing calculation. An overview of the results of plastic plate is then obtained by post-processing calculation. An overview of the results of the calculated forces for different variants of plastic filling and different distances of the the calculated forces for different variants of plastic filling and different distances of the magnet from the plastic plate is given in Figure 12. magnet from the plastic plate is given in Figure 12. As reported in Figure 12, simulated holding forces calculated for different variants of magnetic filling of the plastic plate were, as expected, found to increase with higher infill density with determined values in the range from 4.5 to 6.5 N at zero distance. Such forces are sufficient to ensure a stable attachment of smaller or lighter objects. Thus, the prepared materials can produce components designed to conduct a magnetic flux or a small force interaction and thus attach a certain object. In practice, such elements can then be used in −1 Figure 10. The calculated magnetic field distribution—Magnetic field intensity H (A.m ). The view in detail is shown in the inset. Magnetochemistry 2023, 9, x FOR PEER REVIEW 9 of 13 Figure 9. An image of a computer network model. The actual FEM calculation of the magnetic field distribution corresponds to a mag- netostatic problem with excitation using permanent magnets [54–56]. The result of the simulations is the distributions of the magnetic field in the magnet and the plastic plate with the magnetic filler and the surrounding air. The distribution of Magnetochemistry 2023, 9, 2 9 of 12 magnetic field intensity (H) and magnetic induction (B) for the model with zero air gap are shown in Figures 10 and 11, respectively. The magnitude of the applied force on the plastic plate is then obtained by post-processing calculation. An overview of the results of the construction of magnetic switches or sensors or for the production of components that the calculated forces for different variants of plastic filling and different distances of the homogenize the magnetic field of electric motors. magnet from the plastic plate is given in Figure 12. −1 Magnetochemistry 2023, 9, x FOR PEER R Figure 10. EVIEW The calculated magnetic field distribution—Magnetic field intensity H (A.m ). The 10 of 13 Figure 10. The calculated magnetic field distribution—Magnetic field intensity H (A.m ). The view Magnetochemistry 2023, 9, x FOR PEER R view EVIE in deta W il is shown in the inset. 10 of 13 in detail is shown in the inset. Figure 11. The calculated magnetic field distribution—Magnetic induction B (T). The view in de- Figure 11. The calculated magnetic field distribution—Magnetic induction B (T). The view in de- Figure 11. The calculated magnetic field distribution—Magnetic induction B (T). The view in detail is tail is shown in the inset. tail is shown in the inset. shown in the inset. Figure 12. The calculated magnitudes of holding forces acting on the plastic plate. Figure 12. The calculated magnitudes of holding forces acting on the plastic plate. Figure 12. The calculated magnitudes of holding forces acting on the plastic plate. As reported in Figure 12, simulated holding forces calculated for different variants As reported in Figure 12, simulated holding forces calculated for different variants of magnetic filling of the plastic plate were, as expected, found to increase with higher of magnetic filling of the plastic plate were, as expected, found to increase with higher infill density with determined values in the range from 4.5 to 6.5 N at zero distance. Such infill density with determined values in the range from 4.5 to 6.5 N at zero distance. Such forces are sufficient to ensure a stable attachment of smaller or lighter objects. Thus, the forces are sufficient to ensure a stable attachment of smaller or lighter objects. Thus, the prepared materials can produce components designed to conduct a magnetic flux or a prepared materials can produce components designed to conduct a magnetic flux or a small force interaction and thus attach a certain object. In practice, such elements can then small force interaction and thus attach a certain object. In practice, such elements can then be used in the construction of magnetic switches or sensors or for the production of com- be used in the construction of magnetic switches or sensors or for the production of com- ponents that homogenize the magnetic field of electric motors. ponents that homogenize the magnetic field of electric motors. 4. Conclusions 4. Conclusions This work focused on determining the magnetic properties of PET-G containing mag- This work focused on determining the magnetic properties of PET-G containing mag- netic additive based on Iron(III) and Titanium(II) oxides. The thermal analysis measure- netic additive based on Iron(III) and Titanium(II) oxides. The thermal analysis measure- ments were performed to characterize the thermal behavior of applied polyethylene- ments were performed to characterize the thermal behavior of applied polyethylene- based filaments and to determine the correct set-up of processing temperatures. The prod- based filaments and to determine the correct set-up of processing temperatures. The prod- ucts with different infill densities, and thus various internal architectures, were produced ucts with different infill densities, and thus various internal architectures, were produced using Fused Filament Fabrication technology. using Fused Filament Fabrication technology. Magnetochemistry 2023, 9, 2 10 of 12 4. Conclusions This work focused on determining the magnetic properties of PET-G containing mag- netic additive based on Iron(III) and Titanium(II) oxides. The thermal analysis measure- ments were performed to characterize the thermal behavior of applied polyethylene-based filaments and to determine the correct set-up of processing temperatures. The products with different infill densities, and thus various internal architectures, were produced using Fused Filament Fabrication technology. The paramagnetic properties were identified to be affected by different printed product densities, and relative magnetic permeability was calculated to be increased by up to 40% if samples 100F and 100A were compared. Finite Element Modelling was used to simulate the magnetic field simulations and to calculate the holding forces. Performed FEM model simulations on a typical configuration of a magnet and a plate with magnetic filler showed the creation of a force of around 5 N at zero air gap, which can ensure a stable attachment of objects of smaller dimensions or with lightweight constructions. From the point of view of 3D printing itself, it can be summarized that the price of production can be significantly decreased using the less dense structures due to saving on materials and printing time as well. As a final note, the presented results showed that the properties of produced samples could be tuned according to their desired applications, such as magnetic sensors, switches, and others. It is thanks to choosing the right infill density of the product filling while maintaining the required properties that, as mentioned, it is possible to ensure a cheaper and faster production of shape-demanding samples with cheap FFF technology. The big advantage of this technology is that it is produced without the need to use expensive molds, and the technology is suitable for small-scale production. Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/magnetochemistry9010002/s1; Figure S1: Image for analysis of additive particles using SW ImageJ; Figure S2: TGA graphs for both materials. Author Contributions: Conceptualization, L.Z. and M.M.; methodology, M.M., L.Z. and R.Š.; soft- ware, M.M.; validation, R.Š., J.P. and R.S.; formal analysis, M.M., R.S. and J.P.; Investigation, M.M. and L.Z.; writing—original draft preparation, L.Z., R.Š. and M.M.; writing—review & editing, J.P. and R.Š.; visualization, J.Š.; project administration, J.Š.; funding acquisition, J.P. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Institute of Technology and Business under project 05SVV2203 and the Czech Academy of Sciences, Institute of Theoretical and Applied Mechanics— RVO 68378297. Institutional Review Board Statement: Not applicable. 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Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic Properties

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magnetochemistry Article Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic Properties 1 , 2 , 1 , 3 2 , 4 5 4 4 Lucie Zárybnická * , Martin Marek , Radek Ševc ˇík , Radek Stolín , Jaroslav Pokorný and Jir ˇí Šál Department of Technical Studies, College of Polytechnics Jihlava, Tolstého 16, 586 01 Jihlava, Czech Republic Institute of Theoretical and Applied Mechanics of the Czech Academy of Sciences, Centre Telc, ˇ Prosecká 809/76, 190 00 Praha 9, Czech Republic IT4Innovations, Technical University of Ostrava, Studentská 6231/1B, 708 00 Ostrava-Poruba, Czech Republic Department of Civil Engineering, Faculty of Technology, Institute of Technology and Business, Okružní 517/10, 370 01 Ceské Budejovice, ˇ Czech Republic Department of Mathematics, College of Polytechnics Jihlava, Tolstého 16, 586 01 Jihlava, Czech Republic * Correspondence: [email protected] Abstract: This work aims to characterize printing structures with various infill densities composed of a thermoplastic material containing magnetic particles composed of mainly Iron(III) oxides with regard to their possible processing with the additive technology of Fused Filament Fabrication. A polyethylene terephthalate glycol (PET-G) structural thermoplastic with the addition of Iron(III)) oxides has been selected, and correct processing temperatures have been determined using thermal analysis. The paramagnetic properties of printed products consisting of different filling densities have been tested. Relative permeability has been identified to be strongly dependent on the printed internal structures of tested products. The samples composed of the densest structure have shown relative permeability higher by 18% with respect to the sample printed with the least dense structure. Finite Element Modelling (FEM) simulations have been applied to determine magnetic field distributions and, moreover, to calculate the holding forces of all printed samples. The performed simulations confirmed that produced composites might be utilized as magnetic switches and sensors or as more advanced components for homogenizing electric motors’ magnetic fields. Moreover, magnetic properties might be tuned according to the specific needs printing structure with the suitable density. Citation: Zárybnická, L.; Marek, M.; Ševcík, ˇ R.; Stolín, R.; Pokorný, J.; Šál, Keywords: 3D printing; FFF; PET-G; iron(III) oxide; magnetic properties; FEM simulation J. Effect of Infill Density of the Printed PET-G Structures Containing Iron Oxides on Magnetic Properties. Magnetochemistry 2023, 9, 2. 1. Introduction https://doi.org/10.3390/ Nowadays, additive manufacturing is intensively applied in medicine [1–3], re- magnetochemistry9010002 search [4], engineering [5–7], civil engineering [8], food industries [9], and other industrial Academic Editor: Greg A. Brewer sectors. It represents a prominent way of processing various types of materials [10]. One Received: 22 November 2022 of the most widely used technologies, common in the industry as well as in hobby usage, Revised: 15 December 2022 is Fused Filament Fabrication (FFF), developed by S. Scott Crump in 1989 [11], which Accepted: 18 December 2022 processes filament materials composed of thermoplastics or elastomers. Published: 22 December 2022 FFF additive technology offers a wide range of benefits, such as affordability, suit- ability for both commercial and hobby applications, accessibility of processing materials, and usability for shape-demanding products. An inexhaustible number of different types of thermoplastics and elastomers are currently available for processing. Polylactic acid Copyright: © 2022 by the authors. (PLA) [12–14], polyethylene terephthalate (PET) [15–18], polyethylene terephthalate gly- Licensee MDPI, Basel, Switzerland. col (PET-G) [15,16,19–22], acrylonitrile butadiene styrene (ABS) [23–26], polypropylene This article is an open access article (PP) [27–30], polycarbonate (PC) [31,32], and polyvinylchloride (PVC) [33] belong to the distributed under the terms and most common thermoplastics suitable for processing. conditions of the Creative Commons To improve and/or modify the properties of polymeric materials according to the Attribution (CC BY) license (https:// specific need of their application, various types of additives like UV stabilizers, various creativecommons.org/licenses/by/ fillers, flame retardants, or pigments [34,35] are commonly applied. Last but not least, 4.0/). Magnetochemistry 2023, 9, 2. https://doi.org/10.3390/magnetochemistry9010002 https://www.mdpi.com/journal/magnetochemistry Magnetochemistry 2023, 9, 2 2 of 12 certain additives are also used to improve the magnetic properties of the material. In general, fillers can be applied in the form of particles or fibers. Magnetic particles impart magnetic properties to the polymer composite, conductance, and shielding properties when the basic characteristics describing magnetic properties include magnetic induction, magnetic field intensity, and relative permeability of the material. In this work, PET-G, providing products with, e.g., excellent mechanical properties, ease of use, and sufficient resistance to higher temperatures (compared to the thermoplas- tics ABS and PLA) [36–38], was used. In addition, PET-G usually provides outstanding adhesion between the layers. Moreover, it has minimal risk of twisting and limited shrink- age and can be recycled [39]. PET-G is non-magnetic, which limits its usage for specific applications like components designed to guide and concentrate magnetic flux [40–42] or concentrate magnetic force [43,44]. For these reasons, products containing Iron(III) oxides are used to provide magnetically detectable thermoplastic (MDT) PET-G for the manufacture of sensors and intelligent packaging. This work focused on optimizing the filling density of printed structures composed of PET-G-containing Iron(III) oxides with regard to maintaining the required magnetic characteristics (sufficient permeability values) and material demands needed for processing. Subsequently, the magnetic behavior of developed materials was additionally evaluated by applying Finite Element Modelling (FEM). 2. Materials and Methods 2.1. Materials Grey filaments composed of PET-G containing Iron(III) oxides (Smart Materials 3D, Spain) were used to prepare 3D test samples for subsequent property analysis. The reference sample was printed from black filaments composed of PET-G without magnetic additives (Ø 1.75  0.05 mm, Plasty Mladec, Czech Republic) with a density of 1.27 g.cm . Before usage, materials were conditioned at 50 C for 5 h to remove absorbed water [45]. 2.2. Praparation of Samples The samples were printed as circles (see Figure 1) with a diameter of 60/50 mm (outer/inner) and a height of 20 mm. This shape is conventional for samples used to determine the magnetic properties of ferromagnetic materials using the toroid measurement method [46–50]. A gyroid structure with an infill density of 0, 20, 50, 80, and 100% (Figure 1) was selected. Samples containing the additive were marked according to the filling, namely 0A, 20A, 50A, 80A, and 100A. The reference sample was prepared without any additive with 100% density filling and marked as 100F. The printing temperature was 235 C, whereas the plate temperature was 85 C. The 3D print speed was set to 70 mms . The layer thickness was 0.2 mm, extrusion width 0.4 mm, and skin thickness 0.6 mm—With 1 contour layer. A 3D nozzle with a hole diameter of 0.4 mm was used. Table 1 summarizes all relevant parameters (e.g., printing time and volumes) of the produced samples. At least two duplicates were produced for each sample type. Table 1. Summarization of printing processes for all produced samples. Sample Infill Density/% Printing Time Weight of Filament/g Price/EUR * 0A 0 38 min 3 s 11.3 0.87 20A 20 45 min 8 s 14.2 1.09 50A 50 57 min 38 s 17.0 1.31 80A 80 71 min 5 s 19.4 1.49 100A 100 61 min 34 s 22.9 1.76 100F 100 61 min 34 s 20.4 0.55 * Prices are given as of 14 November 2022. Magnetochemistry 2023, 9, 2 3 of 12 Magnetochemistry 2023, 9, x FOR PEER REVIEW 3 of 13 Figure 1. A diagram of the structures of the prepared samples: (A)—0% filling density, (B)—20% Figure 1. A diagram of the structures of the prepared samples: (A)—0% filling density, (B)—20% filling density, (C)—50% filling density, (D)—80% filling density, (E)—100% filling density. The filling density, (C)—50% filling density, (D)—80% filling density, (E)—100% filling density. The details details of the respective individual types of filling are shown at the bottom right (labeled accord- of the respective individual types of filling are shown at the bottom right (labeled according to the ing to the specific sample). specific sample). Table 1. Summarization of printing processes for all produced samples. 2.3. Methods 3D printing was performed on DeltiX (TriLAB, Czech Republic, nozzle size 0.4 mm), Sample Infill Density/% Printing Time Weight of Filament/g Price/EUR * implementing the FFF technique. A working area of (250  300) mm with an integrated 0A 0 38 min 3 s 11.3 0.87 LCD was applied. Models were created and edited by the FreeCad software and exported in 20A 20 45 min 8 s 14.2 1.09 the .stl format (stereolithography). PrusaSlicer 2.2.0 was used to set the printing parameters 50A 50 57 min 38 s 17.0 1.31 and export them to a post-processing format (*g-code format). 80A 80 71 min 5 s 19.4 1.49 The cross-section of filaments was characterized in terms of surface quality using a 100A 100 61 min 34 s 22.9 1.76 Keyence VHX-6000 optical microscope (Keyence, Itasca, MN, USA) and inspected at 2500 100F 100 61 min 34 s 20.4 0.55 magnification with a focus on the additive distribution. * Prices are given as of 14 November 2022. Additive powders were analyzed for particle size using Keyence VHX-6000 optical microscope (Keyence, Itasca, MN, USA) at 1000 magnification with subsequent analysis 2.3. Methods in the software ImageJ. 3D printing was performed on DeltiX (TriLAB, Czech Republic, nozzle size 0.4 mm), Analyzing the thermal behavior (mass change, heat flow) of the filament samples was implementing the FFF technique. A working area of (250 × 300) mm with an integrated followed by simultaneously performing a Thermogravimetry analysis (TGA) and Differen- LCD was applied. Models were created and edited by the FreeCad software and exported tial thermal analysis (DTA) under non-isothermal conditions, using a TGA 2 instrument in the .stl format (stereolithography). PrusaSlicer 2.2.0 was used to set the printing param- (Mettler-Toledo, Columbus, OH, USA). The measurements were performed in a nitrogen eters and export them to a post-processing format (*g-code format). atmosphere at a heating rate of 20 Cmin , in the temperature range of 30–450 C. The The cros determination s-section of of the filame additive nts was ch content aracte was rize carried d in te out rmon s othe f sur basis face qu of the alitstandar y using a d CSN Keyence EN ISO VHX-6000 optical m 3451-1 [51]. Thr iee croscope replicates (Keyence were ,used Itasca, for M determination. N, USA) and insp The ecte pr d ocedur at 2500 e× magnification with a focus on the additive distribution. consisted of the determination of the combustible proportions when additive content (w, wt.%)Addi usedtive po the calculation wders were by Equation analyzed for p (1): article size using Keyence VHX-6000 optical microscope (Keyence, Itasca, MN, USA) at 1000× magnification with subsequent analysis in the software ImageJ. w = 1  100, (1) Analyzing the thermal behavior (mass change, heat flow) of the filament samples was followed by simultaneously performing a Thermogravimetry analysis (TGA) and Dif- where m is the weight after combustion (g), m is the weight before combustion (g). 1 2 ferential thermal analysis (DTA) under non-isothermal conditions, using a TGA 2 instru- The morphology of samples was investigated with a scanning electron microscope ment (Mettler-Toledo, Columbus, OH, USA). The measurements were performed in a ni- (SEM) Quanta 450 FEG (FEI, Czech Republic) using a secondary electron detector. Observa- −1 trogen atmosphere at a heating rate of 20 °C∙min , in the temperature range of 30–450 °C. tions were conducted on fractured surfaces at 20 kV accelerating voltage. Samples were The determination of the additive content was carried out on the basis of the standard placed on carbon tape and gold coated with a 7 nm thick layer. ČSN EN ISO 3451-1 [51]. Three replicates were used for determination. The procedure X-ray powder diffraction (XRPD) data were collected at 40 kV and 40 mA with a Bragg– consisted of the determination of the combustible proportions when additive content (w, Brentano - diffractometer (Bruker D8 Advance, USA, Cu K radiation ( = 1.5418 Å)). wt.%) used the calculation by Equation (1): Data were collected in the angular range 8–80 2 counting 0.4 s for each step of 0.0102 Magnetochemistry 2023, 9, x FOR PEER REVIEW 4 of 13 𝑚1 (1) 𝑤=(1− )∗100, 𝑚2 where m1 is the weight after combustion (g), m2 is the weight before combustion (g). The morphology of samples was investigated with a scanning electron microscope (SEM) Quanta 450 FEG (FEI, Czech Republic) using a secondary electron detector. Obser- vations were conducted on fractured surfaces at 20 kV accelerating voltage. Samples were placed on carbon tape and gold coated with a 7 nm thick layer. X-ray powder diffraction (XRPD) data were collected at 40 kV and 40 mA with a Bragg–Brentano θ-θ diffractometer (Bruker D8 Advance, USA, Cu Kα radiation (λ = 1.5418 Å)). Data were collected in the angular range 8–80° 2θ counting 0.4 s for each step of 0.0102° 2θ. Rietveld refinements were used for quantitative phase analysis (QPA) using TOPAS 4.2 (Bruker AXS). Magnetic properties were measured on a Remagraph C-500 measuring device (Mag- net-Physik Dr. Steingroever Gmbh, Germany) designed to determine the quasi-stationary (DC) BH hysteresis characteristics of ferromagnetic materials. The configuration of the measuring system Remagraph version C500 is equipped with two electronic fluxmeters EF5. Furthermore, the Remagraph C500 is equipped with a precision DC power supply Magnetochemistry 2023, 9, 2 4 of 12 with a power of 320 VA and parameters ±40 V; ±8 A. The magnitude of the magnetic in- tensity and induction in the measured sample are determined, on the one hand, by the measured material itself and, on the other hand, by the winding configuration (Figure 2). The windings on the samples were made with an insulated copper conductor of full cross- 2. Rietveld refinements were used for quantitative phase analysis (QPA) using TOPAS 4.2 section, where the conductor’s designation was U2 × 0.5. (Bruker AXS). In principle, the magnetizing winding of the measured toroid is connected to a direct Magnetic properties were measured on a Remagraph C-500 measuring device (Magnet- Physik currentDr sour . Steingr ce. The oever curren Gmbh, t is very Germany) slowly incre designed ased and subse to determine quently the de quasi-stationary creased to create (DC) a com BH plehyster te circul esis ation o characteristics f the entire BH of ferr char omagnetic acteristic. T materials. he measur The ing wind configuration ing is connected of the measuring to an electro system nic fluxm Remagraph eter which recor version C500 ds vois ltaequipped ge jitters on with the m twoeelectr asurin onic g win fluxmeters ding and EF5. integra Furthermor tes this vo e,ltthe age. B Remagraph y a joint ev C500 aluais tion o equipped f the ex with citati aon c precision urrent an DCd the power intsupply egrated with a power of 320 VA and parameters 40 V; 8 A. The magnitude of the magnetic voltage, we obtain the resulting BH characteristic—Either only the magnetization or the intensity and induction in the measured sample are determined, on the one hand, by the complete BH hysteresis characteristic [52,53]. An embodiment of the Remagraph measur- measured material itself and, on the other hand, by the winding configuration (Figure 2). ing system and its basic block diagram is shown in Figure 3. Figure 4 shows the principle The windings on the samples were made with an insulated copper conductor of full of determining the magnetic quantities and the individual connections in the toroidal cross-section, where the conductor ’s designation was U2  0.5. sample and the measured material. Figure 2. Photographic images of the testing samples for the magnetic properties measurement, (A)—Samples after 3D printing, (B)—Samples with winding configuration. In principle, the magnetizing winding of the measured toroid is connected to a direct current source. The current is very slowly increased and subsequently decreased to create a complete circulation of the entire BH characteristic. The measuring winding is connected to an electronic fluxmeter which records voltage jitters on the measuring winding and integrates this voltage. By a joint evaluation of the excitation current and the integrated voltage, we obtain the resulting BH characteristic—Either only the magnetization or the complete BH hysteresis characteristic [52,53]. An embodiment of the Remagraph measuring system and its basic block diagram is shown in Figure 3. Figure 4 shows the principle of determining the magnetic quantities and the individual connections in the toroidal sample and the measured material. A simulation program based on the principle of FEM methods, namely the Ansys- Maxwell software (Ansys Inc., Canonsburg, PA, USA), was used to evaluate the magnetic field and holding force of the typical configurations of the permanent magnet and the printed magnetic plastic disc. Ansys-Maxwell is an electromagnetic tool designed to analyze low-frequency problems and devices using the solution of general Maxwell’s equations. The actual simulation of the magnetic field was performed in the program Ansys-Maxwell using FEM calculation methods [54–56]. Magnetochemistry 2023, 9, x FOR PEER REVIEW 5 of 13 Magnetochemistry 2023, 9, x FOR PEER REVIEW 5 of 13 Magnetochemistry 2023, 9, 2 5 of 12 Figure 2. Photographic images of the testing samples for the magnetic properties measurement, Figure 2. Photographic images of the testing samples for the magnetic properties measurement, (A)—Samples after 3D printing, (B)—Samples with winding configuration. (A)—Samples after 3D printing, (B)—Samples with winding configuration. Figure 3. Graphical illustration of remagraph—The basic block diagram of a measuring system. Figure 3. Graphical illustration of remagraph—The basic block diagram of a measuring system. Figure 3. Graphical illustration of remagraph—The basic block diagram of a measuring system. Figure 4. The illustration of the principle of determination of magnetic quantities using toroidal Figure 4. The illustration of the principle of determination of magnetic quantities using toroidal samples. Figure 4. The illustration of the principle of determination of magnetic quantities using toroidal samples. samples. 3. Results and Discussion A simulation program based on the principle of FEM methods, namely the Ansys- A simulation program based on the principle of FEM methods, namely the Ansys- 3.1. Characterization of Material Maxwell software (Ansys Inc., Canonsburg, PA, USA), was used to evaluate the magnetic Maxwell software (Ansys Inc., Canonsburg, PA, USA), was used to evaluate the magnetic XRD analysis revealed that the applied magnetics additive was composed mainly of field and holding force of the typical configurations of the permanent magnet and the field and holding force of the typical configurations of the permanent magnet and the hematite (Iron(III) oxide; 70.7  0.2 wt.%) with 29.3  0.2 wt.% of rutile (Ti(II) dioxide) printed magnetic plastic disc. Ansys-Maxwell is an electromagnetic tool designed to ana- printed magnetic plastic disc. Ansys-Maxwell is an electromagnetic tool designed to ana- based on XRD analysis. Such a combination of mixed oxides compositions exhibits para- lyze low-frequency problems and devices using the solution of general Maxwell’s equa- lyze low-frequency problems and devices using the solution of general Maxwell’s equa- magnetic behavior at room temperature [57]. The mean particle size was calculated to be tions. The actual simulation of the magnetic field was performed in the program Ansys- tions. The actual simulation of the magnetic field was performed in the program Ansys- 160.2  15.3 nm (see Figure S1). The additive content (determined using the combustion Maxwell using FEM calculation methods [54–56]. Maxwell using FEM calculation methods [54–56]. process) was found to be 3.11  0.12 wt.%. The melting point (T ) of both PET-G filaments, with and without the content of metal 3. Results and Discussion 3. Results and Discussion oxides, were determined to select the correct processing temperatures of the extruder and 3.1. Characterization of Material the 3.1. C bed haracteri as wellzation of (Figure Mate S2). T rial he glass transition temperature for this material without addi- XRD analysis revealed that the applied magnetics additive was composed mainly of tives is around 80 C [58]. Setting the temperature around the glass transition temperature XRD analysis revealed that the applied magnetics additive was composed mainly of hematite (Iron(III) oxide; 70.7 ± 0.2 wt.%) with 29.3 ± 0.2 wt.% of rutile (Ti(II) dioxide) for bed temperatures is recommended. One of the first points mentioned in any extrusion hematite (Iron(III) oxide; 70.7 ± 0.2 wt.%) with 29.3 ± 0.2 wt.% of rutile (Ti(II) dioxide) based on XRD analysis. Such a combination of mixed oxides compositions exhibits para- discussion (FFF technology is based on the extrusion process) is the melt temperature. based on XRD analysis. Such a combination of mixed oxides compositions exhibits para- magnetic behavior at room temperature [57]. The mean particle size was calculated to be This is the only temperature that is absolute. The DTA-TGA technique is not sensitive to magnetic behavior at room temperature [57]. The mean particle size was calculated to be 160.2 ± 15.3 nm (see Figure S1). The additive content (determined using the combustion determine T ; therefore, only T was determined. The T was determined to be 244.02 C g m m 160.2 ± 15.3 nm (see Figure S1). The additive content (determined using the combustion process) was found to be 3.11 ± 0.12 wt.%. for the filament containing metal oxides and 235.87 C for the reference sample. process) was found to be 3.11 ± 0.12 wt.%. The melting point (Tm) of both PET-G filaments, with and without the content of The homogeneous distribution of this additive in the PET-G matrix was confirmed The melting point (Tm) of both PET-G filaments, with and without the content of metal oxides, were determined to select the correct processing temperatures of the ex- from its microscopic observations, as can be seen in Figure 5 and detailed in the enclosed in- metal oxides, were determined to select the correct processing temperatures of the ex- truder and the bed as well (Figure S2). The glass transition temperature for this material set figure. The SEM observations showed that applied metal oxides exhibit a high variety in truder and the bed as well (Figure S2). The glass transition temperature for this material shapes and sizes (Figure 6a). Nanosized particles together with micrometric agglomerates were observed. Observations at higher magnifications revealed that larger agglomerates Magnetochemistry 2023, 9, x FOR PEER REVIEW 6 of 13 without additives is around 80 °C [58]. Setting the temperature around the glass transition temperature for bed temperatures is recommended. One of the first points mentioned in any extrusion discussion (FFF technology is based on the extrusion process) is the melt temperature. This is the only temperature that is absolute. The DTA-TGA technique is not sensitive to determine Tg; therefore, only Tm was determined. The Tm was determined to be 244.02 °C for the filament containing metal oxides and 235.87 °C for the reference sam- ple. The homogeneous distribution of this additive in the PET-G matrix was confirmed from its microscopic observations, as can be seen in Figure 5 and detailed in the enclosed inset figure. The SEM observations showed that applied metal oxides exhibit a high vari- Magnetochemistry 2023, 9, 2 6 of 12 ety in shapes and sizes (Figure 6a). Nanosized particles together with micrometric ag- glomerates were observed. Observations at higher magnifications revealed that larger ag- glomerates were composed of nanosized, mainly spherulitic, particles (Figure 6b). The wer intern e composed al structure of nanosized, of the PET-G mainly sample spher witho ulitic,u partic t meta les l p (Figur articles e 6 i b). s visu Theainternal lized in F str iuc- gure 6c. tur Fig e u of re 6d the PET confirmed -G sample the homogenous without metal dis particles tributi is ons visualized of metal in pa Figur rticles e 6w c.ithin a polymer Figure 6d confirmed the homogenous distributions of metal particles within a polymer matrix. matrix. Magnetochemistry 2023, 9, x FOR PEER REVIEW 7 of 13 Figure 5. Microscopic image of the microstructure of the used PET-G filament containing metal Figure 5. Microscopic image of the microstructure of the used PET-G filament containing metal oxides. oxides. Figure 6. The collection of SEM images: (a)—Particles of metal oxides observed at lower magnifi- Figure 6. The collection of SEM images: (a)—Particles of metal oxides observed at lower magnifica- cation,(b)—Microstructure of metal oxides particles observed at higher magnification, (c)—Inter- tion, (b)—Microstructure of metal oxides particles observed at higher magnification, (c)—Internal nal structure of PET-G sample, (d)—Internal structure of PET-G sample containing additive. structure of PET-G sample, (d)—Internal structure of PET-G sample containing additive. 3.2. Magnetic Properties As expected, the prepared PET-G samples containing magnetic fillers showed para- magnetic behavior [59]. The measured BH hysteresis characteristic is thus reduced to a straight line, and the resulting characteristic magnetic parameter corresponds to the rela- tive permeability. Figure 7 shows the magnetization characteristics for all types of pro- duced samples with 0–100% filling density. The clear difference between samples 100A and 100F (REF) is visible. In the case of sample A, only small differences can be observed with the increasing filling density. A determined value of relative permeability was found to increase slightly with higher filling density: 1.24, 1.29, 1.34, 1.35, and 1.39 for samples 0A, 20A, 50A, 80A, and 100A, respectively. Such values were determined to be at least 18 % higher if compared with the REF sample (1.05). Figure 7. Resulting in magnetization characteristics of individual samples. Magnetochemistry 2023, 9, x FOR PEER REVIEW 7 of 13 Figure 6. The collection of SEM images: (a)—Particles of metal oxides observed at lower magnifi- cation,(b)—Microstructure of metal oxides particles observed at higher magnification, (c)—Inter- nal structure of PET-G sample, (d)—Internal structure of PET-G sample containing additive. Magnetochemistry 2023, 9, 2 7 of 12 3.2. Magnetic Properties As expected, the prepared PET-G samples containing magnetic fillers showed para- 3.2. Magnetic Properties magnetic behavior [59]. The measured BH hysteresis characteristic is thus reduced to a As expected, the prepared PET-G samples containing magnetic fillers showed para- straight line, and the resulting characteristic magnetic parameter corresponds to the rela- magnetic behavior [59]. The measured BH hysteresis characteristic is thus reduced to a tive permeability. Figure 7 shows the magnetization characteristics for all types of pro- straight line, and the resulting characteristic magnetic parameter corresponds to the relative duced samples with 0–100% filling density. The clear difference between samples 100A permeability. Figure 7 shows the magnetization characteristics for all types of produced and 100F (REF) is visible. In the case of sample A, only small differences can be observed samples with 0–100% filling density. The clear difference between samples 100A and 100F with the increasing filling density. A determined value of relative permeability was found (REF) is visible. In the case of sample A, only small differences can be observed with the to incr incr ea easing se slig filling htly wi density th higher f . A determined illing densi value ty: 1.of 24r, elative 1.29, 1. permeability 34, 1.35, and was 1.39 found for sam to ples increase slightly with higher filling density: 1.24, 1.29, 1.34, 1.35, and 1.39 for samples 0A, 0A, 20A, 50A, 80A, and 100A, respectively. Such values were determined to be at least 18 20A, 50A, 80A, and 100A, respectively. Such values were determined to be at least 18 % % higher if compared with the REF sample (1.05). higher if compared with the REF sample (1.05). Figure 7. Resulting in magnetization characteristics of individual samples. Figure 7. Resulting in magnetization characteristics of individual samples. 3.3. Magnetic Field Simulation and Calculation of Force Effects The basic possible usage of printed magnetic plastics is related to the emergence of a certain force effect on the finished material upon its exposure to an external magnetic field [60]. In common and technical practice, there are certainly applications where it is necessary to attach a general plastic structure to a magnet or other source of a magnetic field. Conversely, attaching the magnetic elements to the plastic base may also be beneficial. In simple terms, it may be an alternative to a sheet metal magnetic board. The key question for subsequent practical applications is how large can be the achieved force. The find the answer to this question, this subchapter presents the results of the magnetic field simulation and calculation of force effects on the model of the selected type configuration of a permanent magnet and type plastic plate corresponding to variants of printed PET-G with different levels of filling. During the simulation, different distances of the magnet from the plastic plate, ranging from 0 to 5 mm, were considered. The model was conceived as 2D axisymmetric and corresponded to the cylindrical design of the permanent magnet and the plastic plate. The permanent magnet had a diameter of 20 mm and a height of 3 mm. The plastic plate with a magnetic filler had a diameter of 100 mm and a thickness of 5 mm. The surroundings of the model were air with a diameter of 240 mm and a height of 120 mm. The permanent magnet was considered to be the FeNdB type, version N35, with a coercive force (Hc) equal to 890 Kam . The design of the model is graphically visualized in Figures 8 and 9, where the basic model for the zero distance of the magnet and the plastic plate is shown. Magnetochemistry 2023, 9, x FOR PEER REVIEW 8 of 13 3.3. Magnetic Field Simulation and Calculation of Force Effects The basic possible usage of printed magnetic plastics is related to the emergence of a certain force effect on the finished material upon its exposure to an external magnetic field [60]. In common and technical practice, there are certainly applications where it is neces- sary to attach a general plastic structure to a magnet or other source of a magnetic field. Conversely, attaching the magnetic elements to the plastic base may also be beneficial. In simple terms, it may be an alternative to a sheet metal magnetic board. The key question for subsequent practical applications is how large can be the achieved force. The find the answer to this question, this subchapter presents the results of the magnetic field simula- tion and calculation of force effects on the model of the selected type configuration of a permanent magnet and type plastic plate corresponding to variants of printed PET-G with different levels of filling. During the simulation, different distances of the magnet from the plastic plate, rang- ing from 0 to 5 mm, were considered. The model was conceived as 2D axisymmetric and corresponded to the cylindrical design of the permanent magnet and the plastic plate. The permanent magnet had a diameter of 20 mm and a height of 3 mm. The plastic plate with a magnetic filler had a diameter of 100 mm and a thickness of 5 mm. The surroundings of the model were air with a diameter of 240 mm and a height of 120 mm. The permanent magnet was considered to be the FeNdB type, version N35, with a coercive force (Hc) −1 Magnetochemistry 2023, 9, 2 equal to 890 Ka·m . The design of the model is graphically visualized in Figures 8 and 9, 8 of 12 where the basic model for the zero distance of the magnet and the plastic plate is shown. Magnetochemistry 2023, 9, x FOR PEER REVIEW 9 of 13 Figure 8. The FEM model of the permanent magnet and plastic plate with a magnetic filler. Figure 8. The FEM model of the permanent magnet and plastic plate with a magnetic filler. Figure 9. An image of a computer network model. Figure 9. An image of a computer network model. The actual FEM calculation of the magnetic field distribution corresponds to a magne- The actual FEM calculation of the magnetic field distribution corresponds to a mag- tostatic problem with excitation using permanent magnets [54–56]. netostatic problem with excitation using permanent magnets [54–56]. The result of the simulations is the distributions of the magnetic field in the magnet The result of the simulations is the distributions of the magnetic field in the magnet and the plastic plate with the magnetic filler and the surrounding air. The distribution of and the plastic plate with the magnetic filler and the surrounding air. The distribution of magnetic field intensity (H) and magnetic induction (B) for the model with zero air gap magnetic field intensity (H) and magnetic induction (B) for the model with zero air gap are shown in Figures 10 and 11, respectively. The magnitude of the applied force on the are shown in Figures 10 and 11, respectively. The magnitude of the applied force on the plastic plate is then obtained by post-processing calculation. An overview of the results of plastic plate is then obtained by post-processing calculation. An overview of the results of the calculated forces for different variants of plastic filling and different distances of the the calculated forces for different variants of plastic filling and different distances of the magnet from the plastic plate is given in Figure 12. magnet from the plastic plate is given in Figure 12. As reported in Figure 12, simulated holding forces calculated for different variants of magnetic filling of the plastic plate were, as expected, found to increase with higher infill density with determined values in the range from 4.5 to 6.5 N at zero distance. Such forces are sufficient to ensure a stable attachment of smaller or lighter objects. Thus, the prepared materials can produce components designed to conduct a magnetic flux or a small force interaction and thus attach a certain object. In practice, such elements can then be used in −1 Figure 10. The calculated magnetic field distribution—Magnetic field intensity H (A.m ). The view in detail is shown in the inset. Magnetochemistry 2023, 9, x FOR PEER REVIEW 9 of 13 Figure 9. An image of a computer network model. The actual FEM calculation of the magnetic field distribution corresponds to a mag- netostatic problem with excitation using permanent magnets [54–56]. The result of the simulations is the distributions of the magnetic field in the magnet and the plastic plate with the magnetic filler and the surrounding air. The distribution of Magnetochemistry 2023, 9, 2 9 of 12 magnetic field intensity (H) and magnetic induction (B) for the model with zero air gap are shown in Figures 10 and 11, respectively. The magnitude of the applied force on the plastic plate is then obtained by post-processing calculation. An overview of the results of the construction of magnetic switches or sensors or for the production of components that the calculated forces for different variants of plastic filling and different distances of the homogenize the magnetic field of electric motors. magnet from the plastic plate is given in Figure 12. −1 Magnetochemistry 2023, 9, x FOR PEER R Figure 10. EVIEW The calculated magnetic field distribution—Magnetic field intensity H (A.m ). The 10 of 13 Figure 10. The calculated magnetic field distribution—Magnetic field intensity H (A.m ). The view Magnetochemistry 2023, 9, x FOR PEER R view EVIE in deta W il is shown in the inset. 10 of 13 in detail is shown in the inset. Figure 11. The calculated magnetic field distribution—Magnetic induction B (T). The view in de- Figure 11. The calculated magnetic field distribution—Magnetic induction B (T). The view in de- Figure 11. The calculated magnetic field distribution—Magnetic induction B (T). The view in detail is tail is shown in the inset. tail is shown in the inset. shown in the inset. Figure 12. The calculated magnitudes of holding forces acting on the plastic plate. Figure 12. The calculated magnitudes of holding forces acting on the plastic plate. Figure 12. The calculated magnitudes of holding forces acting on the plastic plate. As reported in Figure 12, simulated holding forces calculated for different variants As reported in Figure 12, simulated holding forces calculated for different variants of magnetic filling of the plastic plate were, as expected, found to increase with higher of magnetic filling of the plastic plate were, as expected, found to increase with higher infill density with determined values in the range from 4.5 to 6.5 N at zero distance. Such infill density with determined values in the range from 4.5 to 6.5 N at zero distance. Such forces are sufficient to ensure a stable attachment of smaller or lighter objects. Thus, the forces are sufficient to ensure a stable attachment of smaller or lighter objects. Thus, the prepared materials can produce components designed to conduct a magnetic flux or a prepared materials can produce components designed to conduct a magnetic flux or a small force interaction and thus attach a certain object. In practice, such elements can then small force interaction and thus attach a certain object. In practice, such elements can then be used in the construction of magnetic switches or sensors or for the production of com- be used in the construction of magnetic switches or sensors or for the production of com- ponents that homogenize the magnetic field of electric motors. ponents that homogenize the magnetic field of electric motors. 4. Conclusions 4. Conclusions This work focused on determining the magnetic properties of PET-G containing mag- This work focused on determining the magnetic properties of PET-G containing mag- netic additive based on Iron(III) and Titanium(II) oxides. The thermal analysis measure- netic additive based on Iron(III) and Titanium(II) oxides. The thermal analysis measure- ments were performed to characterize the thermal behavior of applied polyethylene- ments were performed to characterize the thermal behavior of applied polyethylene- based filaments and to determine the correct set-up of processing temperatures. The prod- based filaments and to determine the correct set-up of processing temperatures. The prod- ucts with different infill densities, and thus various internal architectures, were produced ucts with different infill densities, and thus various internal architectures, were produced using Fused Filament Fabrication technology. using Fused Filament Fabrication technology. Magnetochemistry 2023, 9, 2 10 of 12 4. Conclusions This work focused on determining the magnetic properties of PET-G containing mag- netic additive based on Iron(III) and Titanium(II) oxides. The thermal analysis measure- ments were performed to characterize the thermal behavior of applied polyethylene-based filaments and to determine the correct set-up of processing temperatures. The products with different infill densities, and thus various internal architectures, were produced using Fused Filament Fabrication technology. The paramagnetic properties were identified to be affected by different printed product densities, and relative magnetic permeability was calculated to be increased by up to 40% if samples 100F and 100A were compared. Finite Element Modelling was used to simulate the magnetic field simulations and to calculate the holding forces. Performed FEM model simulations on a typical configuration of a magnet and a plate with magnetic filler showed the creation of a force of around 5 N at zero air gap, which can ensure a stable attachment of objects of smaller dimensions or with lightweight constructions. From the point of view of 3D printing itself, it can be summarized that the price of production can be significantly decreased using the less dense structures due to saving on materials and printing time as well. As a final note, the presented results showed that the properties of produced samples could be tuned according to their desired applications, such as magnetic sensors, switches, and others. It is thanks to choosing the right infill density of the product filling while maintaining the required properties that, as mentioned, it is possible to ensure a cheaper and faster production of shape-demanding samples with cheap FFF technology. The big advantage of this technology is that it is produced without the need to use expensive molds, and the technology is suitable for small-scale production. Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/magnetochemistry9010002/s1; Figure S1: Image for analysis of additive particles using SW ImageJ; Figure S2: TGA graphs for both materials. Author Contributions: Conceptualization, L.Z. and M.M.; methodology, M.M., L.Z. and R.Š.; soft- ware, M.M.; validation, R.Š., J.P. and R.S.; formal analysis, M.M., R.S. and J.P.; Investigation, M.M. and L.Z.; writing—original draft preparation, L.Z., R.Š. and M.M.; writing—review & editing, J.P. and R.Š.; visualization, J.Š.; project administration, J.Š.; funding acquisition, J.P. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Institute of Technology and Business under project 05SVV2203 and the Czech Academy of Sciences, Institute of Theoretical and Applied Mechanics— RVO 68378297. Institutional Review Board Statement: Not applicable. 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Journal

Magnetochemistry – Multidisciplinary Digital Publishing Institute

Published: Dec 22, 2022

Keywords: 3D printing; FFF; PET-G; iron(III) oxide; magnetic properties; FEM simulation

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